The present invention relates to sequentially ordered biodegradable lactide (or glycolide or lactide/glycolide)/xcex5-caprolactone multi-block copolymers having proper degradation properties and enhanced mechanical properties such as flexibility and elasticity and a process for the preparation thereof. The present invention further relates to biodegradable materials comprising the multi-block copolymers having proper hydrolytic properties and enhanced mechanical properties.
With heightened interest in biodegradable polymer materials for medical application, research thereto is hurriedly under way. These materials include natural biodegradable polymers and synthetic biodegradable polymers. Natural biodegradable polymers include polypeptides such as collagen and gelatin; polyamino acids such as poly-L-glutamic acid and poly-L-lysine; and polysaccharides such as alginic acid and chitin. Natural biodegradable polymers have poor resulting mechanical properties and are difficult to process and mass-produce.
Accordingly, there is a need for research on synthetic polymers. Among key materials in this research are aliphatic polyesters that have both excellent physical properties and excellent hydrolytic properties. However, these synthetic polymers must satisfy requirements including biostability, biocompatibility, low toxicity, and low immunogenicity as they are to be used in the human body. Therefore, research is restricted to materials that are either approved by authorities such as the FDA or known to be biologically compatible. Biodegradable synthetic polymers commonly and currently used include polycaprolactone (PCL), polyglycolide (PG), polylactide (PL) and their derivatives such as lactide/glycolide copolymer and lactide/xcex5-caprolactone copolymer.
Further, the need for more flexible and more elastic biodegradable materials has increased since biodegradable polymers such as polyglycolide, polylactide, and lactide/glycolide copolymer, actively researched at present, are hard materials. Attempts at making softer and more elastic copolymers by copolymerizing lactide and glycolide with soft xcex5-caprolactone are still deficient. This copolymer exists in the form of either random or block copolymer (U.S. Pat. No. 4,057,537). The limited physical properties of the copolymer restrict its usefulness as a biodegradable material, especially as a regeneration material of human tissues or organs because such material requires various physical properties.
The sequentially ordered biodegradable multi-block copolymer shows a variety of new physical properties that conventional materials do not have. Further, xcex5-caprolactone block in such copolymer provides elasticity to the material as a soft segment beyond the softening effect on the hard polylactide. This elastic material is will be very effective in assisting regeneration of elastic tissues such as tissues of skeletal muscle, smooth muscle and cardiac muscle, because these tissues need very strong elasticity.
According to the present invention, there is provided a biodegradable lactide (or glycolide or lactide/glycolide)/xcex5-caprolactone multi-block copolymer with proper biodegradability and enhanced mechanical properties such as flexibility and elasticity, and a method for preparing the same.
The biodegradable multi-block copolymer is of Formula 1, which is as follows. 
wherein,
A is polylactide (PL), polyglycolide (PG), or polylactide/polyglycolide (PL/PG), PCL is poly xcex5-caprolactone, and
n is an integer from 2 to 2,000.
The present method for preparing the biodegradable multi-block copolymer of Formula 1, comprises the steps of:
providing a polylactide (or polyglycolide or polylactide/polyglycolide) and poly xcex5-caprolactone; introducing acylhalide functional groups to both terminals of said polylactide (or polyglycolide or polylactide/polyglycolide); and
coupling the acylhalide functional groups located at the terminals of the polylactide (or polyglycolide or polylactide/polyglycolide) with the corresponding hydroxyl functional groups located at the terminals of the poly xcex5-caprolactone.
The molecular weight of the multi-block copolymer may be from about 2,000 to 500,000 daltons. The molecular weight of the polylactide, polyglycolide or poly xcex5-caprolactone may be about 500 to 30,000 daltons. The composition molar ratio of lactide, glycolide or lactide/glycolide to xcex5-caprolactone is about 1/9 to 9/1, and preferably, the composition molar ratio of lactide to xcex5-caprolactone is 1/9 to 9/1.
The present invention provides medical materials such as matrix for medical use and wound covering made from these lactide (or glycolide or lactide/glycolide)/xcex5-caprolactone copolymers.
The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawing.